Research Sheds Light On Origins, Age Of Massive Impact Crater

Research sheds light on origins, age of massive impact crater (phys.org)
https://phys.org/news/2021-06-age-m...VaCZtbb61R3oLMvWx6_AVMdW_erbSlN4FS_8M0KbbBkUs

JUNE 1, 2021
Research sheds light on origins,

age of massive impact crater

by Sharon Oosthoek, University of Western Ontario

Greenland's Ice Sheet From 40,000 Feet. Credit: NASA
Hidden beneath a kilometer of ice in northwestern Greenland,
an impact crater that could swallow a city the size of London, Ont.
is the subject of much debate about its origins and age.


Now, Western planetary scientist Elizabeth Silber has published new research suggesting the crater could be young—as craters go—having formed during the Pleistocene geological epoch, between 11,700 and 2.6 million years ago.

The impact of the asteroid thought to have created the Hiawatha crater
would have produced so much heat that the ice sheet would have released
a massive volume of meltwater "in pretty much an instant," Silber said.

She estimates it would have produced enough water to fill Lake Tahoe,
which straddles California and Nevada.

"It is a rarity to find a new impact crater on Earth, let alone one of this size,"
said Silber, an adjunct professor with Western's department of earth sciences.

"While some 190 impact structures have been cataloged thus far,
this putative crater is interesting because it looks geologically young
and well preserved and, if confirmed, it will be among the largest
ever found on Earth," she said.

"Because it is hiding beneath the ice sheet it begs the question (of) when it might have formed, and whether the ice existed at the time."

The 31-kilometer-wide crater first came to the world's attention in 2018
when a team led by the University of Copenhagen published research
revealing its existence.

The discovery sparked a lively debate about whether
the two-kilometer-wide asteroid believed to have made it hit
before or after the Greenland Ice Sheet formed about 2.6 million years ago.

"Because it is very well preserved, it points to a possibly very young age,
as young as the onset of the Younger Dryas period
(between 11,500 and 14,500 years ago)," said Silber.

"Or alternatively, if old, it tells us about the erosional processes
that might have taken place in that area."
Silber studies how impact craters form on various planetary bodies, including Jupiter's moon Europa, Saturn's moon Titan, our moon, and Earth.

She also studies the physics of meteors, or shooting stars.

So, she was well placed to put together a team, including some
of the researchers who made the initial discovery,
to shed light on the crater's formation and age.

The team used hydrocode modeling, a numerical tool that describes the physics behind the shockwaves that cause impact craters to form. The modeling takes into account the projectile's composition, target and impact speed, as well as surface temperature and other factors.

"Modeling formation of impacts into terrestrial ice sheets has never been done before, and it serves to shed light on why the crater is unusual in terms of morphology and why the rocky ejecta is absent from drill cores," Silber said.

Shockwave physics assume that an impact this big should form a peak-ring basin with a pronounced crater rim if an asteroid slams directly into bedrock.

But the Hiawatha crater has a central uplift and muted morphology, which means that the crater rim is less pronounced. The formation of the central uplift makes sense, however, if an asteroid hit at a time when the land was covered
with ice at the height of the sheet's thickness (likely 1.5 to 2 kilometers).

"The modeling shows that thick overlying ice in fact serves to muffle the formation of a peak-ring basin," said Silber. "Furthermore, the nearby drill cores don't show any rocky ejecta from the impact, and our study shows that ice sheets inhibit ejection of rocky material during the impact."

While it wasn't the focus of her paper, Silber calculated some of the likely after-effects of a large asteroid slamming into the ice sheet.

She came up with a dramatic picture: supersonic winds of 400 kilometers an hour ripping down trees within a 200-kilometer radius and stripping them of branches and leaves. Anyone within a 500-kilometer radius would have seen a white-hot fireball that appeared four times larger than the sun, she said.

"From a scientific standpoint, we want to know how something might have occurred and how it might have affected the region. After all, the Chixculub impact, which was significantly larger than the Hiawatha impact, was responsible for wiping out the dinosaurs some 65 million years ago."

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Explore further
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More information: Elizabeth A. Silber et al, Effect of ice sheet thickness on formation of the Hiawatha impact crater, Earth and Planetary Science Letters (2021). DOI: 10.1016/j.epsl.2021.116972
Journal information: Earth and Planetary Science Letters

Provided by University of Western Ontario



Research sheds light on origins, age of massive impact crater (phys.org)
https://phys.org/news/2021-06-age-m...VaCZtbb61R3oLMvWx6_AVMdW_erbSlN4FS_8M0KbbBkUs

 

Graham Hancock
25m ·

QUOTE: "Because it is very well preserved, it points to a possibly very young age,
as young as the onset of the Younger Dryas period (between 11,500 and 14,500 years ago)." END QUOTE

My prediction: As the research into the Hiawatha Crater continues,
the final date for its creation will come in at around 12,800 to 12,900 years ago,
which is the correct date for the onset of the Younger Dryas
(not 14,500 years as erroneously stated in the linked article),
and the causative agent will be confirmed not as an asteroid
but as a fragment of the disintegrating comet that caused devastation
all around the world and initiated the Younger Dryas.

This global cataclysm, on the cusp of the Upper Palaeolithic and the Neolithic,
has profound implications for the possibility of a lost civilization of the Ice Age.

For more see my books Magicians of the Gods (2015) and America Before (2019).